G. Ciavola

Results and interpretation of high frequency experiments at 28 GHz in ECR ion sources, future prospects

For the needs of future heavy ion accelerators, electron cyclotron resonance ion sources (ECRISs) should be able to deliver higher intensities and higher charge states. The 1e mA level intensity has already been reached by room temperature ECRIS for medium charge states of light elements (O6+, Ar8+). However, such level of intensity for heavy elements (like Pb27+ for CERN/LHC and GSI) requires more powerful ECRIS with higher electron densities (up to 1013 cm−3). On the other hand, an optimized magnetic configuration system has to be used in order to obtain the suitable compromise between the electron confinement and the high flux ion losses. Before the design of the future “high intensity ECRIS,” experiments have been performed with the superconducting SERSE source both at 18 and 28 GHz. After an overview of major results recently obtained, some scaling laws will be presented. Our results show that much larger intensities and charges can be reached with ECRIS. Then, we will show how the next ECRIS generat...

Operation of the SERSE superconducting electron cyclotron resonance ion source at 28 GHz

The SERSE source [P. Ludwig et al., Rev. Sci. Instrum. 69, 4082 (1998), and references therein] is a superconducting electron cyclotron resonance (ECR) ion source, operating at the Laboratori Nazionali del Sud in Catania since 1998; it is currently used as the main injector for the K-800 superconducting cyclotron. Its high magnetic field provides a high plasma confinement and large currents of highly charged ions, as compared to conventional sources. It can efficiently operate at the microwave frequency of 14 and 18 GHz [S. Gammino and G. Ciavola, Rev. Sci. Instrum. 71, 631 (2000); S. Gammino et al., ibid.70, 3577 (1999)] and has been used as a test bench for injection at 28 GHz. High-frequency operation is expected to create a higher plasma density, thus resulting in larger currents of multiply charged ions. In this article, we report the first operation of an ECR ion source at 28 GHz by using a gyrotron. The gyrotron itself and the waveguide line are described, along with the operational results (in xen...

Metallic etching by high power Nd:yttrium–aluminum–garnet pulsed laser irradiation

A Nd:yttrium–aluminum–garnet pulsed laser, with 1064 nm wavelength, 9 ns pulse width, and 0.9 J maximum pulse energy, is employed to irradiate in vacuum different metal targets (Al, Ti, Ni, Cu, Ta, W, Au, and Pb). In order to measure the erosion thresholds, the etching rates, and the chemical yields, a mass quadrupole spectrometer is interfaced to the vacuum chamber. Etching process shows a threshold, which ranges between 0.1 and 1.6 J/cm2 for lead and tungsten, respectively. Etching rates range between 0.3 and 10 μg/pulse for copper and lead, respectively. The irradiation produces chemical yields ranging between 0.04 and 0.6 atoms/100 eV for copper and lead, respectively. A simple theoretical approach is presented to justify obtained results. The objective of collected data concerns the possibility to use ejected atoms, neutral and ionized, in an electron cyclotron resonance ion source, in order to provide high current, multiply charge ion beams.

Angular distribution of ejected atoms from Nd:YAG laser irradiating metals

A Nd:YAG pulsed laser is employed to irradiate different metals in vacuum at the ECLISSE facility of the Laboratorio Nazionale del Sud, Catania, INFN. Laser pulse energy, 9 ns in width, ranges between 100 and 900 mJ. The ejection of atoms by means of laser irradiation is studied in terms of angular distribution, laser etching yield and film thickness deposited on a substrate. Light elements (Ni, Cu) show an angular distribution that is larger than heavy ones (W, Pb). A theoretical approach, applied to fit experimental data, indicates that the distribution depends on the high power of cos θ and that the flow velocity of ejected atom ranges between 27 000 and 88 000 m/s and the kinetic energy of ejected species ranges between 0.7 and 4.4 keV.

Observations of the frequency tuning effect in the 14 GHz CAPRICE ion source

A set of measurements with the CAPRICE ion source at the GSI test bench has been carried out to investigate its behavior in terms of intensity and shape of the extracted beam when the microwaves generating the plasma sweep in a narrow range of frequency (+/-40 MHz) around the klystron center frequency (14.5 GHz). Remarkable variations have been observed depending on the source and the beamline operating parameters, confirming that a frequency dependent electromagnetic distribution is preserved even in the presence of plasma inside the source. Moreover, these observations confirm that the frequency tuning is a powerful method to optimize the electron cyclotron resonance ion source performances. A description of the experimental setup and of the obtained results is given in the following.

Angular distribution of ions emitted from Nd:YAG laser-produced plasma

Angular distribution of ion currents emitted from laser-produced plasmas are reported for a Nd:YAG laser with intensities lower than 1×1010 W/cm2. This distributions are strongly peaked along the normal to the target surface for Cu, Sn, Ta, W, Au, and Pb ion streams, independent of the incidence angle of the irradiated target. For Al, Ni, and Nb the main axis tends to decline to about −10°. The comparison of fits of Gaussian function and cosP(α−α0)+y0 to the experimental data verified the formal equivalency of both the functions. Fitted values of the FWHM and of the exponent P are compared for all the elements used. The angular distribution of mean ion velocity 〈v〉 and ion kinetic energy 〈E〉 are presented.

Review on high current 2.45 GHz electron cyclotron resonance sources (invited)

The suitable source for the production of intense beams for high power accelerators must obey to the request of high brightness, stability, and reliability. The 2.45 GHz off-resonance microwave discharge sources are the ideal device to generate the requested beams, as they produce multimilliampere beams of protons, deuterons, and monocharged ions, remaining stable for several weeks without maintenance. A description of different technical designs will be given, analyzing their strength, and weakness, with regard to the extraction system and low energy beam transport line, as the presence of beam halo is detrimental for the accelerator.

Production of low energy, high intensity metal ion beams by means of a laser ion source

The ECLISSE (ECR coupled to Laser Ion Source for charge State Enhancement) project started in 1999 with the aim to obtain an intense beam of highly charged ions (pulsed mode) by means of the coupling between a laser ion source (LIS) and an electron cyclotron resonance (ECR) ion source. The major points to be investigated appeared to be the coupling efficiency between the ion beam produced by the LIS and the ECR plasma, as well as the possibility to enhance the available charge state by an ECRIS with respect to the standard methods which are used to produce ion beams from solid samples (e.g., evaporation, sputtering). The calculations have confirmed that this concept may be effective, provided that the ion energy from the LIS is lower than a few hundred eV. The main features of the calculations will be shown, along with the results obtained in the off-line test facility at laser power densities below 1011 W/cm2.

Preliminary tests for the electron cyclotron resonance ion source coupled to a laser ion source for charge state enhancement experiment

At the Laboratori Nazionali del Sud we have designed a hybrid ion source, consisting of a laser ion source as first stage, which gives intense currents of electrons and of multiply charged ions, followed by an electron cyclotron resonance (ECR) ion source as a second stage, which should act as a charge state multiplier. The ECR ion source coupled to a laser ion source for charge state enhancement (ECLISSE) experiment has been funded by INFN and preliminary experiments have been carried out at IPPLM in Warsaw, in order to confirm the beneficial effects of the axial magnetic field of the ECR ion source on the extraction of the ions from the LIS, as foreseen by calculations. The description of the ECLISSE experiment and of the results of the preliminary tests will be reported.

18 GHz upgrading of the superconducting electron cyclotron resonance ion source SERSE

The superconducting electron cyclotron resonance ion source SERSE of INFN-Laboratori Nazionali del Sud has been recently upgraded with an 18 GHz generator which takes the place of the 14.5 GHz generator, used up to now. In order to further extend the validation of high B mode to higher frequency, some comparative tests have also been carried out, aimed at understanding the role of the magnetic field and frequency on the ion yield at higher levels than were ever done before. The results at the frequencies of 14.5 and 18 GHz are compared and the trend already observed elsewhere is here confirmed. Preliminary observations of the “two frequency heating” have contributed to increase further the currents of the highest charge states.The superconducting electron cyclotron resonance ion source SERSE of INFN-Laboratori Nazionali del Sud has been recently upgraded with an 18 GHz generator which takes the place of the 14.5 GHz generator, used up to now. In order to further extend the validation of high B mode to higher frequency, some comparative tests have also been carried out, aimed at understanding the role of the magnetic field and frequency on the ion yield at higher levels than were ever done before. The results at the frequencies of 14.5 and 18 GHz are compared and the trend already observed elsewhere is here confirmed. Preliminary observations of the “two frequency heating” have contributed to increase further the currents of the highest charge states.